Shading Solar Panels, Series Or Parallel?

Whether you have an off-grid homestead, RV, van, or even a sailboat, shading can significantly reduce the power output of your panels. The fact is that shade is the enemy of solar panels. In this article we will consider how you can remedy shading on your solar panels.

Why is shading on solar panels so bad?

Shade has an effect on current, while temperature has an effect on voltage. When there is shade on solar panels it will reduce the current of that panel. Unfortunately, if you have a single panel, there is really nothing you can do about this.

Let’s say you have a panel that has a rating of 17.5 Volts and 5.8 Amps, it will produce 100Watts.

Now if shade comes over the panel, the current could drop to 3 Amps, but the voltage stays the same, resulting in 52.5 Watts (3 Amps x 17.5 Volts).

What Is The Effect Of Shaded PV Cells In Series And Parallel?

If you have multiple solar panels they can be connected in series or parallel. In most cases they are connected in series. Solar panels should always be wired in series if there is not a shading problem, and the total voltage stays under the charge controller max input voltage. However, If you expect to have shade on your panels, adding panels in series is not the best configuration. If there is shade on one panel, the current will drop. In a series connection, the current will take the lowest value in the string. See image below.

Diagram sourced from Clever Solar Power.

The shaded spot on one panel will decrease the string of panels to 3 amps at 52.5 volts. This means that the total power will be reduced from 300 Watts (52.5 Volts x 5.8 Amps) to 157 Watts (52.5 Volts x 3 Amps).

Let’s look at what parallel does.

If we do the same experiment with parallel connections, we see that we have a higher power output. This is because in parallel connections voltage stays the same but current is added together. 

Solar irradiance (sunshine) only has an impact on the current and not on voltage. So , if we add 3 amps + 5.8 amps + 5.8 amps to become 14.6 amps total. If we multiply this by the voltage of 17.5 we become 255 Watts which is higher than the 157 Watts in a series connection.

Diagram sourced from Clever Solar Power.

If shading is something you expect from your panels, putting them in a parallel configuration is recommended. If you wire your panels in parallel, the current is higher which means you need to increase the wire diameter. This will increase the cost of your solar system. Therefore, you need to include a combiner box and make the distance between the combiner box and the charge controller as short as possible.

What Type Of Solar Panel Works Best In Shade?

There is no significant difference in how both technologies handle shaded conditions. With improvements in solar panel technology, Monocrystalline and Polycrystalline panels are basically the same. If you want to get technical, However, polycrystalline technology has a bigger surface area than monocrystalline for the same amount of power generation.

In conclusion, if shading is not going to be a problem for you, you can wire your panels in series. It is easier to install, more cost effective and better for your MPPT solar charge controllers performance. However, if you have a caravan or RV and are on the move, parallel connection would be a better option. This is because you can not always be certain if there is going to be sunshine all the time on your panels. Yes, it will cost you more in wiring, but it will pay off in the long term. Especially if your battery bank is running low.